It has long been known that the flue gas produced at coal-burning facilities and power plants contains dangerous levels of toxic SO.sub.2 gas. Many methods have been advanced over the years as a means of desulfurizing the emissions from such facilities.
U.S. Pat. Nos. 4,931,264 and 4,804,521 proposed the use of a system which combines Ca(OH).sub.2 and fly ash to solve this problem. The process disclosed by these patents involves contacting the sulfur-containing gas with a slurry containing a calcium alkali and a calcium-reactive silica or alumina which has been heated to a temperature sufficient to produce the sulfur-absorbing components. While this process is effective for removing sulfur from flue gas, it has a number of drawbacks. Among these drawbacks is the fact that only some of the components of the reaction mixture are capable of yielding products that can take up SO.sub.2 efficiently. Thus, much of the sorbent produced is composed of species which do not take up SO.sub.2 efficiently. The average percent conversion or utilization of the calcium for groups of representative Ca(OH).sub.2 -fly ash sorbents made from Illinois, Appalachian, and Powder River basin fly ashes is only 42%, 48%, and 52% as measured with a sandbed sorption test apparatus loaded with 1 g of sorbent and 40 g of sand through which a gas composed of 1000 ppm of SO.sub.2 in N.sub.2 at a temperature of 64.degree. C. and a relative humidity of 60% is passed at a flow rate of 5 L/min for 1 hour. This is disclosed in Singer et al., "Suitability of Available Fly Ashes In Advocate Sorbents" 1991 EPRI-EPA-DOE SO.sub.2 Control Symposium. Some of the species which do not take up SO.sub.2 efficiently are toxic, and all must ultimately be disposed of. The transportation of spent sorbent and other byproducts and the subsequent disposal thereof is very costly and will become more costly as disposal sites become filled.
It has remained for the subject invention to solve the foregoing problems by the development of a process which uses a reactant containing Ca.sub.3 SiO.sub.5 admixed with about 3% of a compound such as CaSO.sub.4 .multidot.2H.sub.2 O that facilitates the conversion of the Ca.sub.3 SiO.sub.5 to the desired product, or Ca.sub.2 SiO.sub.4, or both the admixture and Ca.sub.2 SiO.sub.4, preferably ordinary Portland cement, as an ingredient in a process that produces a finely divided product whose main active components include C--S--H and Ca(OH).sub.2.
Therefore, it is an object of the subject invention to provide a process which uses a readily available starting ingredient to produce a desulfurization product.
It is another object of this invention to produce a finely divided product whose main active components include C--S--H and Ca(OH).sub.2.
It is yet another object of this invention to produce a sorbent which has a percent conversion or utilization of its calcium of better than about 50% under specified conditions common in the industry and set forth hereinafter, with an apparatus loaded with 0.5 g of sorbent and 20 g sand through which a gas composed of 2000 ppm of SO.sub.2 in N.sub.2 at temperature of 60.degree. C. and a relative humidity of 60% is passed at a flow rate of 1 L/min for 1 hour.
It is yet another object of this invention to produce a sorbent containing only small amounts of species which take up SO.sub.2 inefficiently and which are hazardous.
It is a further object of this invention to provide a desulfurization sorbent which is recyclable once spent.